Well, I never stopped in mid-traffic to ask, until recently: apparently the lady concerned couldn't see my indicators. You, know, I can see the logic in that, as the rear lights are quite low and the front indicators are not easy to see in daylight. I tested this in Google Sketchup and again using my wife's car: as you can see from the pictures, one may not be able to see the ute lights if the ute is nearby.
What I really needed was indicators higher up and further forward, without making a permanent fix until I'd tested the idea. Here is what I did.
Screwdrivers, Philips #2 and #1
* "Beautey", as in "Yeah, she's a real beauty, mate". In the US of A these are called pickup trucks.
Step 1: Procure the Lights
If you don't have one, these boards are easy enough to make if you have basic DIY skills and there are any number of trailer lights that fit the purpose. The white plank on mine has a hollow ribbed core, much like the cross section of synthetic decking*, which allows for the wiring to be hidden. The lights can be bought from any good automotive store or possibly a good hardware store.
This should also be possible in cars using after-market lights positioned high on the rear window. There are kits like this and window pads that you can buy online, or possibly at the automotive store. I thought there might be suction-cup window lights for sale somewhere, but even the Internet hasn't helped there.
A permanent installation need not use a board, of course: lights could be fitted to the deck rack itself and a cable taken down inside the uprights to be properly wired into the lighting wiring loom (I would use an auto electrician to do this). If a board is used then once mounted properly, the board could be easily removed for it's original purpose.
(* you could probably use a length of this as a board for this project if you like).
Step 2: (Re)wire the Connector and Make Sure All the Lights Work
As you can see from the attached pictures, the standard wiring plan hasn't changed much in the last 35 years! In this case there are only five wires and I didn't need the "Service brakes", so I used the blue wire for the rear red and front white (side marker) lights instead of the usual brown wire.
A couple of bulbs were burnt out but fortunately I had a selection in my workshop, so avoided a trip to the store.